1. Field of the Invention
The present invention relates to apparatus for electronically testing printed circuit boards or the like. Such apparatus includes a plurality of substantially parallel test pins or test probes for making electrical contact between respective contact areas on a printed circuit board or the like to be tested and a plurality of corresponding resilient contact elements disposed in accordance with a grid of an array plate or the like against which the apparatus is urged, and a mask plate extending at right angles to the test pins and having therein through-bores through which extend the test pins. First ends or tips of the test pins project through the through-bores in the mask plate to engage the contact areas of the printed circuit board. Such apparatus may include a very large number of such generally parallel test pins or test probes, e.g., 20,000 or more.
Apparatus of the above type is rather fully described in Driller et al., U.S. Pat. No. 4,721,908 and Mang et al., U.S. Pat. No. 4,834,659. The principal object of the present invention is to afford improvements over the devices disclosed in the foregoing patents, particularly relative to the design of the test probes, and the manner of retaining such test probes in the apparatus, while readily permitting their removal if desired.
In the apparatus disclosed in Driller et al., U.S. Pat. No. 4,721,908, an elastic plate in the nature of a rubber sheet is provided for mounting the plurality of test probes. In such an arrangement, the test probes are in the nature of straight pins without any enlarged or reduced sections. The elastic plate is in the nature of a rubber sheet through which the plurality of test pins are pressed so as to perforate the sheet and thereby mount the test pin. In the foregoing known device, the elastic plate or sheet firmly engages the periphery of each of the test pins extending therethrough, and in that manner prevents them from dropping from the testing apparatus.
One disadvantage of the foregoing device is that movement of one test pin can influence movement of several other adjacent test pins due to the manner in which they are mounted in the elastic or rubber sheet in close spacing to one another. Thus, in use of such a device, if one test pin is urged in a longitudinal direction, several other pins could be caused to move with it, which is a disadvantage. It must be borne in mind that such an apparatus may include several thousand such test pins or test probes, and it is preferable that each pin be capable of longitudinal movement independently of the others.
In the apparatus of Mang et al., U.S. Pat. No. 4,834,659, there is disclosed a different means of supporting the test pins which represents an attempt to solve the problem discussed above where longitudinal movement of a single test pin can cause similar movement of adjacent pins. In the Mang et al. patent, straight test pins are not used. Instead, each test pin is provided with an enlarged section of relatively short length. One form of enlargement comprises a section which is hammered or deformed. As a result, the normally round test pin will have a flattened area which is enlarged.
In the Mang et al. patent, various types of enlarged pin sections are disclosed, but in each case the concept is the same. The pins are mounted in a pair of inner and outer adapter plates formed with a large number of holes or bores which normally would conform to the connection points to be tested on a printed circuit board or the like. Such bores are larger in diameter than the outer diameter of the test pins, but smaller in diameter than the enlarged section of each test pin. The pins are assembled so that the enlarged pin sections are disposed between the inner and outer adapter plates, thereby trapping the pins relative to the two adapter plates and preventing them from falling out of the test apparatus.
The main object of the present invention is to provide an improved type of test pin which is neither straight nor has an enlarged section, but rather has a section which is reduced in size compared to the normal pin diameter.
A related object of the invention is to provide improved apparatus for retaining test pins or test probes in a testing device which effectively retains the pins in the desired positions, permits independent longitudinal movement of one pin relative to adjacent pins, and yet readily permits removal of pins from the apparatus when desired, such advantages being achieved without providing any enlarged sections along the length of a test pin.
An important advantage of the present invention in comparison with test pins having enlarged sections is that it permits the pins to be arrayed in closer proximity to one another. It is highly desirable to be able to provide for greater miniaturization or closer spacing of the test pins, because the industry is continuing to seek higher density in printed circuit boards and associated components, with the result that apparatus for electronically testing such printed circuit boards requires closer spacing of the thousands of test pins or test probes.
The foregoing and other objects and advantages of the invention will be apparent from the following description of certain preferred embodiments thereof, taken in conjunction with the accompanying drawings.